The present invention relates to methods and compositions for use in subterranean operations. More particularly, in certain embodiments, the present invention relates to methods of altering the viscosity of a subterranean treatment fluid with a cyclodextrin modifier.
Treatment fluids may be used in a variety of subterranean operations, including, but not limited to, drilling operations, stimulation, sand-control, fluid-diversion treatments, and cementing operations. As used herein, the term “treatment,” or “treating,” refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The term “treatment,” or “treating,” does not imply any particular action by the fluid or any particular component thereof.
Polymeric gelling agents, such as guar gums, cellulose derivatives, biopolymers, polysaccharides, synthetic polymers, and the like, have previously been added to treatment fluids to obtain a desired viscosity. Viscoelastic surfactants have also been added to treatment fluids to increase the viscosity thereof. For example, gels can be formed by the association of hydrophobic portions of surfactants to form micelles or larger associative structures. The micelles or other associative structures increase the viscosity of the base fluid and may provide viscoelastic characteristics to the fluid in cases where the surfactant structure is suitably chosen. Similarly, hydrophobically modified (“HM”) polymers have been utilized to increase the viscosity of aqueous treatment fluids. As used herein, the term water-soluble relative permeability modifier. As used herein, the term “HM polymer” refers to a polymer with hydrophobic groups incorporated into a hydrophilic polymer structure while retaining water solubility. As used herein, a polymer is considered water soluble with at least 0.01 weight percent soluble in distilled water and, preferably, at least 5-10 weight percent soluble in distilled water. For instance, intermolecular associative micellar bonds may be formed between hydrophobic groups on a different polymer chain, which result in a three-dimensional associated network, akin to a cross-linked network structure, that thereby increases the viscosity of the fluids. Surfactants may be used to promote the formation of these micellar bonds among HM polymer chains. As used herein, the terms “micellar associations” and “micellar bonds” refer to those associative interactions between hydrophobic groups on HM polymers molecules.
Maintaining sufficient viscosity in these treatment fluids may be important for a number of reasons. For example, maintaining sufficient viscosity is important in fracturing and sand-control treatments for particulate transport and/or to create or enhance fracture width. Also, maintaining sufficient viscosity may be important to control and/or reduce fluid loss into the formation. Moreover, a treatment fluid of a sufficient viscosity may be used to divert the flow of fluids present within a subterranean formation (e.g., formation fluids, other treatment fluids) to other portions of the formation, for example, by “plugging” an open space within the formation. At the same time, while maintaining sufficient viscosity of the treatment fluid often is desirable, it also may be desirable to maintain the viscosity of the treatment fluid in such a way that the viscosity may be reduced at a particular time, inter alia, for subsequent recovery of the fluid from the formation.